The present invention relates to a gas supply apparatus and, more particularly, to a gas supply apparatus for supplying a gas having a vapor pressure lower than the atmospheric pressure to a vacuum vessel which is evacuated.
FIG. 3 shows a piping system for explaining a conventional gas supply apparatus. As shown in FIG. 3, a conventional gas supply apparatus 6 includes a bomb 1 filled with a gas, a source valve 2 for performing supply/interruption of the gas, a pipe 7 connected to a vacuum device 9, a heater 13 for heating the pipe 7 and the source valve 2. The gas supply apparatus 6 supplies the gas to a vacuum vessel 10 evacuated to a predetermined pressure, e.g., 0.05 atm, in the vacuum device 9 through a mass flow controller 4 for automatically controlling a gas flow rate. Reference numeral 12 denotes a vacuum pump arranged in the vacuum device 9, and reference numerals 14 to 16 denote valves for interrupting gas.
Since the vacuum device 9 is generally separated from the gas supply apparatus in a dustproof room, the pipe 7 for supplying a liquid gas having a vapor pressure lower than the atmospheric pressure to the vacuum device 9 is set to be long. For this reason, attention must be paid to a change in temperature and temperature distribution of the pipe 7. That is, a pressure in the pipe 7 up to the mass flow controller 4a is relatively high, and a temperature in the pipe 7 is lower than that in the bomb 1. For this reason, gas is liquefied, and the liquid gas is filled in the pipe 7, thereby causing gas supply to be difficult. In order to prevent this, a pipe portion extending from the outlet of the bomb 1 to the mass flow controller 4 in the vacuum device main body 9 must be wound by the heater 13 such that the temperature in the pipe 7 is kept at a constant temperature higher than a temperature in the bomb 1 or such that the temperature in the pipe 7 and the bomb 1 is kept at a constant temperature higher than the ambient temperature.
In this conventional gas supply apparatus, the following problems are posed during installation and maintenance of a gas pipe. Since an entire gas pipe extending from the gas supply apparatus to a vacuum device main body must be wound by a heater wire, installation and maintenance costs are increased. In addition, since the temperature of the long pipe must always be controlled to be constant, a temperature abnormality monitoring system must be mounted, thereby complicating routine management.